Oma210000 Gsm Principles Issue4.10

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Course Code
GSM Principles
Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
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Objectives
Upon completion of this course, you will be able to:
Grasp basic idea of GSM system such as frequency spectrum, frequency reuse etc.
Grasp the structure of the GSM system and the protocol used.
Grasp certain numbers that refer to BSS
Grasp the 4 kinds of channel combination and understand the idea of multi-frame.
Know some radio techniques
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References
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Contents
Radio Techniques
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Contents
Radio Techniques
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GSM system overview
The GSM system is a frequency- and time-division cellular system, each physical channel is characterized by a carrier frequency and a time slot number
Cellular systems are designed to operate with groups of low-power radios spread out over the geographical service area. Each group of radios serve MSs presently located near them. The area served by each group of radios is called a CELL
Uplink and downlink signals for one user are assigned different frequencies, this kind of technique is called Frequency Division Duplex (FDD)
Data for different users is conveyed in time intervals called slots , several slots make up a frame. This kind of technique is called Time Division Multiple Access (TDMA)
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System was named as Global System for Mobile Communication
GSM system began to provide service in Europe(2G)
Provide services for the whole world
Micro Cell Technique is used in GSM system
1989
1991
1992
1994
1996
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Macro Cell and Micro Cell
A certain radio coverage area formed by a set of transceivers that connected to a set of antennas is called a CELL.
Macro Cell
In the beginning , High-Power BTSs are adopted to provide services. The BTS covers a wider area , but its frequency utilization is not efficient. So , it can only provide a few channels for subscribers.
Micro Cell
Later the Low-Power BTS joins the system for getting a better service area with high capacity . At the same time it adopts the frequency reuse technique to improve the efficiency of the frequency utilization and also the whole capacity of the network.
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Multiple Access Technique
Multiple Access Technique allows many subscribers to use the same communication medium.
There are three kinds of basic Multiple Access Technique : FDMA , TDMA and CDMA.
GSM system adopt FDD-TDMA (FDMA and TDMA together).
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FDMA
FDMA uses different frequency channels to accomplish communication.
The whole frequency spectrum available is divided into many individual channels (for transmitting and receiving)every channel can support the traffic for one subscriber or some control information.
Frequency
Time
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TDMA
TDMA accomplishes the communication in different timeslot.
A carrier is divided into channels based on time. Different signals occupy different timeslots in certain sequence , that is , many signals are transmitted on the same frequency in different time.
Time
Frequency
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CDMA
CDMA accomplishes the communication in different code sequences.
Special coding is adopted before transmission, then different information will lose nothing after being mixed and transmitted together on the same frequency and at the same time.
Time
Frequency
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Fd(n)=Fu(n)+45
Fd(n)=Fu(n)+45
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The frequency resource of mobile system is very limited.
The different Subscribers can use the same frequency in different places.
The quality of communication must be ensured.
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Contents
Radio Techniques
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– Mobile Equipment
– Subscriber Identity Module
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Location Area Identity (LAI)
Subscriber Authentication Key (Ki)
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The Trans-coder – TC and Sub multiplexer (SM)
BTS
BSC
TC/SM
BSS
MSC
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BTS
BSC
TC/SM
BSS
MSC
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Inter-working : communication between different entities inside the GSM network
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Supplementary service information
Subscriber status (registered/deregistered)
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Location Area Identity(LAI)
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If NOT found
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Contents
Radio Techniques
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LAI
The LAI is the international code for a location area.
MCC: Mobile Country CodeIt consists of 3 digits .
For example: The MCC of China is "460"
MNC: Mobile Network CodeIt consists of 2 digits .
For example: The MNC of China Mobile is "00"
LAC: Location Area CodeIt is a two bytes hex code.
The value 0000 and FFFF is invalid.
For example: 460-00-0011
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CGI
The CGI is a unique international identification for a cell
The format is LAI+CI
LAI: Location Area Identification
CI: Cell Identity. This code uses two bytes hex code to identify the cells within an LAI.
For example : 460-00-0011-0001
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BSIC
NCC: PLMN network color code. It comprises 3 bit. It allows various neighboring PLMNs to be distinguished.
BCC: BTS color code. It comprises 3 bit, used to distinguish different cells assigned the same frequency!
BSICBase Station Identification Color Code)
NCC
BCC
BSIC
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MSISDN
CC: Country Code. For example: The CC of China is "86".
NDC: National Destination Code. For example: The NDC of China Telecom is 139, 138, 137, 136, 135.
SN: Subscriber Number. Format:H0 H1 H2 H3 ABCD
Example: 86-139-0666-1234
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IMSI
For example: The MCC of China is "460"
MNC: Mobile Network CodeIt consists of 2 digits .
For example: The MNC of China Telecom is "00"
MSIN: Mobile Subscriber Identification Number. H1H2H3 S ABCDEF
For example: 666-9777001
NMSI: National Mobile Subscriber IdentificationMNC and MSIN form it together.
For Example of IMSI : 460-00-666-9777001
Not more than 15 digits
3 digits
2 digits
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TMSI
The TMSI is assigned only after successful subscriber authentication.
The VLR controls the allocation of new TMSI numbers and notifies them to the HLR.
TMSI is used to ensure that the identity of the mobile subscriber on the air interface is kept secret.
The TMSI consists of 4 bytes( 8 HEX numbers) and determined by the operator.
TMSI: Temporary Mobile Subscriber Identification)
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IMEI
IMEI: International Mobile Station Equipment Identification
TAC: Type approval code, 6 bit, determined by the type approval center
FAC: Final assembly code, 2 bit, It is determined by the manufacturer.
SNR: Serial number, 6 bits, It is issued by the manufacturer of the MS. SP: 1 bit , Not used.
Check the IMEI in your MS : *#06#
TAC
FAC
SNR
SP
IMEI
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Contents
Radio Techniques
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The physical channel is the medium over which the information is carried: 200KHz and 0.577ms
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slot is called a “burst”
The logical channel consists of the information carried over the physical channels
TDMA FRAME
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Traffic Channel (TCH) :
Control Channel (CCH) :
Or Signaling Channel, transmits all kinds of control information.
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TCH/9.6 Data Channel 9.6kb/s
TCH/4.8 Data Channel 4.8kb/s
TCH/2.4 Data Channel 2.4Kb/s
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is monitored by the MS
periodically when it is in idle mode
BCCH: Broadcast Control Channel
FCCH: Frequency Correction Channel
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CCH
CCCH
RACH
uplink
CBCH
downlink
PCH/AGCH
downlink
The CCCH is responsible for transferring control information between all mobiles and the network.
RACH: Random Access Channel
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CCH
DCCH
SDCCH
FACCH
SACCH
DCCH is assigned to a single wireless connection for measurement and handover purpose.
SDCCH: Stand-alone Dedicated Control Channel
ACCH: Associated Control Channel
ACCH
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Allocate signaling channel
Search for synchronous burst
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Packet service channel (PDTCH)
Packet control channel
Private control channel: PACCH, PTCCH
BCCH
TCH
SACCH
CCCH
TCH
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SDCCH combination – SDCCH/8 + SACCH/8
TCH/FR combination – TCH/F + FACCH/F + SACCH/F
TCH/HR combination – TCH/H + FACCH/H + SACCH/H
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Combination of packet logic channel
Packet logic channels (PDCH) can be combined via the following three modes
Mode 1: PBCCH+PCCCH+PDTCH+PACCH+PTCCH;
Mode 2: PCCCH+PDTCH+PACCH+PTCCH;
Mode 3: PDTCH+PACCH+PTCCH
In case of small GPRS traffic, GPRS and circuit services use the same BCCH and CCCH in the cell. In this case, only combination mode 3 is needed in the cell
With the increase of traffic, the packet public channel should be configured in the cell. Channel combination mode 1 and mode 2 should be adopted
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Contents
Radio Techniques
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8W
0.8W
5W
Both Uplink and Downlink power settings can be controlled independently and individually.
BCCH -------
10.unknown
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send the signal in advance!
When the MS is in idle mode, the time sequence within the MS can be adjusted via the SCH channel. However, the mobile station does not know how far it is away from the base station. If the distance between the MS and the base station is 30km, the time sequence of the MS will be 100μs slower than that of the base station. When the mobile phone sends its first RACH signal, it is already 100μs later. For there is still another 100μs of transmission delay, when the signal reaches the base station, the total delay is 200μs . It is very possible that the signal collides with the pulse of the adjacent timeslot around the base station. Therefore, RACH and some other channel access pulses will be shorter than other pulses. Only after receiving the time sequence adjustment signal (TA) from the base station, MS can send pulses of normal length. In this case, the MS needs to send signals by 200μs in advance.
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Diversity – What’s Diversity?
Receive diversity provides an effective technique for both overcoming the impact of fading across the radio channel and increasing the received signal to interference ratio.
The former is achieved by ensuring “uncorrelated” (i.e. low enough correlated) fading between antenna branches i.e. not all antennas experience fades at the same time.
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Contents
Radio Techniques
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8PSK
GMSK
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Summary
The frequency spectrum used in GSM
The structure of GSM
Some radio techniques used in GSM
Evolution of GSM

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Oma210000 Gsm Principles Issue4.10